Method of using 1H-pyrimido-4,5-c -1,2-diazepines as antibacterial and anticoccidocidal agents

ABSTRACT

Compounds of the general formula (I) ##STR1## wherein R 1  and R 2  are selected from a lower alkyl group, a phenyl group (optionally substituted by one or more hydroxy or lower alkoxy groups), a pyridyl group or a group --CO 2  R where R is a lower alkyl group, (provided that when R 1  is a group --CO 2  R, R 2  is a lower alkyl group) are disclosed. 
     The compounds of formula (I) are useful as intermediates to compounds of other ring systems which are of pharmacological interest. 
     Certain of the compounds of formula (I) are also useful as antimicrobial agents.

This is a division of application Ser. No. 926,072 filed July 19, 1978 now abandoned.

This invention relates to 1H-pyrimido{4,5-c}-1,2-diazepines, methods of their preparation, compositions and formulations containing them and their uses as antimicrobial agents, and as intermediates for heterocyclic transformations.

The present invention provides novel 1H-pyrimido{4,5-c}-1,2-diazepines of formula (I), or their tautomers, or salts thereof, ##STR2## wherein R¹ and R² are the same or different and are selected from a lower alkyl group, a phenyl group (optionally substituted by one or more hydroxyy or lower alkoxy groups), a pyridyl group or a group CO₂ R in which R is a lower alkyl group; provided that when R¹ is a group CO₂ R then R² may only be a lower alkyl group.

The term "lower" as used herein in conjunction with an alkyl or alkoxy group is indicative of the fact that such groups have from 1 to 4 carbon atoms arranged in a straight or branched chain.

It is to be understood that compounds where tautomerism is possible between, on the one hand, a hydroxy group and an oxo group, and on the other hand, an amino group and an imino group, at a particular position on the (1H)-pyrimido{4,5-c}-1,2-diazepines of formula (I), the more stable forms are respectively, the oxo group and the amino group. The formulae used in the present specification show the more stable form of such compounds.

It should be noted that the compounds of formula (I) possess a completely new type of skeletal ring structure, that is, the pyrimido{4,5-c}-1,2-diazepine bicyclic rings. Accordingly, an important advantage of the present invention is that a whole new area of novel chemistry has been opened up for further investigation by the provision herein of processes enabling the production of compounds of formula (I).

The above compounds of formula (I) have been found to be particularly susceptible to ring-opening and ring-closure rearrangement reactions. Depending upon the nature of the substituents, their location, and reaction conditions, the compounds of the present invention may be converted to either pyrido{2,3-d}-pyrimidines, pyrimido{4,5-c}pyridazines, or pyrazolo{2,3-d}pyrimidines which compounds may then be converted by reactions well known in the art, for example hydrolysis, halogenation, amination, reduction, oxidation, nucleophilic substitution, electrophilic substitution and elimination, to compounds with the same basic skeletal ring structure but different substitutents which compounds have biological activity. For example, the pyrido{2,3-d}-pyrimidines of U.K. Patent Specification Nos. 774 094 and 774 095 have activity against lactic acid bacteria, the pyrido{2,3-d}pyrimidines of U.K. Patent Specification No. 1 129 084 are useful as diuretics, the pyrido{2,3-d}pyrimidines of U.K. Patent Specification No. 1 427 508 are active against micro-organisms which utilise the de novo synthesis of riboflavin, the pyrazolo{2,3-d}pyrimidines of U.K. Patent Specification No. 798 646 are active as antimetabolites in purine synthesis, and pyrimido{4,5-c}pyridazines have activity as inhibitors of the enzyme dihydropteroate synthetase which enables micro-organisms to synthesise an essential intermediate in the production of tetrahydrofolate co-factors. The compounds of the present invention may therefore be used as intermediates for the production of pharmaceuticals which have one of the above three specified ring structures.

Within the class of (1H)-pyrimido{4,5-c}-1,2-diazepines of formula (I) there is a group of compounds represented by formula (II): ##STR3## wherein R³ is a phenyl group optionally substituted with one or more hydroxy groups; and R⁴ is a group CO₂ R in which R is as hereinbefore defined, which exhibit dihydropteroic acid biosynthesis inhibitory activity.

Thus, the above compounds of formula (II) inhibit one of the enzymes, namely dihydropteroate synthetase, which enables micro-organisms to synthesise an essential intermediate in the production of tetrahydrofolate co-factors. Most of these co-factors are one-carbon adducts of tetrahydrofolic acid and they are essential metabolites in cells for the biosynthesis of purines, thymidylic acid, serine and several other biologically important compounds. Man and other higher animals are unable to synthesise folic acid and therefore they have to obtain it from food which contains the required preformed folates.

On the other hand, most micro-organisms synthesise folic acid from simpler chemicals. Generally the biosynthetic process first provides `dihydropteridine` (Pt), i.e. 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine (HMPt) pyrophosphate ester, from its immediate precursor HMPt in the presence of the enzyme hydroxymethyldihydropteridine pyrophosphokinase (HMPPS). Pt then condenses with p-aminobenzoic acid (pAB) in the presence of the enzyme dihydropteroate synthetase to form dihydropteroic acid (DPtA). This intermediate further condenses with a glutamate to form dihydrofolic acid (DFA or `folate`) which is then enzymatically reduced to produce the essential tetrahydrofolate.

As examples of compounds which are particularly active and fall within this class are 8-amino-3-carbethoxy-1-methyl-5-phenyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one and 8-amino-3-carbomethoxy-1-methyl-5-(3-hydroxyphenyl)-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one. These compounds additionally have the ability to potentiate the antimicrobial activity of a 2,4-diamino-5-benzyl pyrimidine and/or a sulphonamide, for example trimethoprim or sulphamethoxazole.

Also within the class of (1H)-pyrimido{4,5-c}-1,2-diazepines of formula (III): ##STR4## wherein R' is a phenyl group optionally substituted with one or more lower alkoxy groups and R" is a group --CO₂ R in which R is as hereinbefore defined, or a phenyl group which have anti-protozoal, for example anti-coccidial, activity.

As examples of compounds falling within formula (III) and of particular interest are 8-amino-3-carbomethoxy-1-methyl-5-(3,4,5-trimethoxyphenyl)-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one; 8-amino-3-carbethoxy-1-methyl-5-(2,4-dimethoxyphenyl)-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one and 8-amino-3,5-diphenyl-1-methyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one. Such compounds alternatively have the ability to potentiate the antimicrobial activity of combinations of a 2,4-diamino-5-benzylpyrimidine and a sulphonamide. Thus compounds of formula (III) may for example, potentiate the antiprotozoal activity of a mixture of diaveridine and sulphaquinoxaline.

The compounds of formula (I) may be prepared by the reaction of 6-(1-methylhydrazino)isocytosine, represented by formula (IV): ##STR5## with an α,γ-dicarbonyl compound of formula (V): ##STR6## wherein R¹ and R² are as hereinbefore defined.

The preparation is suitably achieved by refluxing in a suitable solvent, most desirably a hydroxylic solvent such as a C₁ -C₄ alkanol, glacial acetic and/or water, at a reflux temperature for up to several days. Optimally the reaction is carried out in refluxing methanol.

In the preparation of compounds of formula (I) some other bicyclic compound may be formed as a by-product. In such instances it may be necessary to isolate the required compound by the usual procedures known in the art.

The reaction of the compound of formula (IV) with those of formula (V) is a two-step process, the first step being a condensation reaction and the second step a cyclisation of the so formed intermediate. It is believed that the intermediate formed has the formula (VI): ##STR7## wherein R¹ and R² are as hereinbefore defined. The compounds of formula (VI) are novel compounds which form a further aspect of the invention. It is to be understood that the compounds of formula (VI) may either be converted in situ to compounds of formula (I) by continuing the reaction to completion under the original conditions or alternatively may be isolated and then converted to compounds of formula (I) under the reaction conditions suitable for the direct conversion of the intermediate to compounds of formula (I).

The type of dicarbonyl compound of formula (V) used in the preparation of compounds of formula (I) will of course depend upon the substituents R¹ and R² in the compounds of formula (I).

Thus when R¹ is either a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or a pyridyl group and R² is a group CO₂ R in which R is a lower alkyl group, viz a compound of formula (VII): ##STR8## where R is as defined above and R⁵ is a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or a pyridyl group, the dicarbonyl compound will be an α,γ-diketoester of formula (VIII): ##STR9## where R and R⁵ are as defined hereinabove. In this case the believed intermediate is a compound of formula (IX): ##STR10## where R and R⁵ are as defined hereinabove. Compounds of formula (IX) are novel and form a further aspect of the invention.

When in the compounds of formula (I), R¹ and R² are the same and are both a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or a pyridyl group, viz a compound of formula (X): ##STR11## where R⁶ is a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or a pyridyl group, then the dicarbonyl compound will be a symmetrical 1,3-diketone of formula (XI):

    R.sup.6 --CO.CH.sub.2.CO.R.sup.6                           (XI)

where R⁶ is as defined above. In this case the intermediate will be a compound of formula (XII): ##STR12## where R⁶ is as defined above. Compounds of formula (XII) are novel and form a further aspect of the present invention.

When, in the compounds of formula (I), R¹ is a lower alkyl group and R² is a group CO₂ R in which R is a lower alkyl group, viz a compound of formula (XIIIa): ##STR13## where R is as hereinbefore defined and R⁷ is a lower alkyl group or, alternatively R¹ is a group CO₂ R where R is a lower alkyl group and R² is a lower alkyl group, viz a compound of formula (XIIIb): ##STR14## when R and R⁷ are as defined above, the the diketo compound will be an α,γ-diketo ester of formula (XIV):

    R.sup.7 COCH.sub.2.COCO.sub.2 R                            (XIV)

where R and R⁷ are as defined above. The reaction of a compound of formula (XIV) with the compound of formula (IV) always leads to a mixture of condensation products, believed to be compounds of formula (XV): ##STR15## where R and R⁷ are as hereinbefore defined and formula (XVI): ##STR16## where R and R⁷ are as hereinbefore defined.

The compounds of formulae (XV) and (XVI) may either be separated from each other, for example by column chromatography before conversion into compounds of formulae (XIIIa) and (XIIIb) respectively, or preferably they may be cyclised together and the so produced isomeric compounds (XIIIa) and (XIIIb) may be separated from each other by methods known in the art for separating isomeric compounds, for example by column chromatography on, for instance, silica gel.

The compounds of formulae (XV) and (XVI) are novel compounds which form further aspects of the present invention.

Compounds of formula (I) wherein R¹ is a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or a pyridyl group and R² is a group CO₂ R in which R is as hereinbefore defined may be converted to pyrido{2,3-d}pyrimidines by saponification at room temperature followed by acidification to pH 2.0 to 5.0 to yield the carboxylic acid corresponding to the starting ester and subsequent heating to 100° to 150° C. in an alkyl cellosolve or in dimethyl sulphoxide. Thus according to a further aspect of the present invention there is provided a method of making a compound of formula (XVIIa): ##STR17## where R⁸ is a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or a pyridyl group which comprises heating in an alkyl cellosolve or in dimethyl sulphoxide, a compound of formula (XVIII): ##STR18## wherein R⁸ is as hereinbefore defined.

The compounds of formulae (XVII) and (XVIII) are novel and constitute further aspects of the present invention.

The saponification of a compound of formula (I) wherein R¹ is a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or, pyridyl group and R² is a group CO₂ R in which R is as hereinbefore defined may conveniently be carried out using an aqueous alkali, for example aqueous sodium hydroxide. The subsequent acidification step which produces the corresponding compound of formula (XVIII) is conveniently performed using an aqueous acid, preferably an aqueous inorganic acid, for example hydrochloric acid.

The alkyl cellosolve in which compounds of formula (XVIII) may be heated to produce compounds of formula (XVII) is preferably methyl cellosolve, and the heating should be carried out for 2-3 hours at 100° to 150° C., most preferably at 125° C. Preferably the compound of formula (XVIII) is separated from the reaction medium in which it is produced before it is heated to produce ring rearrangement.

Compounds of formula (I) wherein (a) R¹ is a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or apyridyl group and R² is a group CO₂ R in which R is a lower alkyl group; or (b) R¹ and R² are the same and each is a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or apyridyl group may be converted to pyrazolo{3,4-d}pyrimidines by heating in aqueous acid at a temperature of greater than 70° C. Thus according to a further aspect of the present invention there is provided a process of making a compound of formula (XIX): ##STR19## wherein R⁹ is a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or a pyridyl group which comprises heating in aqueous acid a compound of formula (XX): ##STR20## wherein (a) R¹⁰ is a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or a pyridyl group and R¹¹ is a group CO₂ R in which R is as hereinbefore defined; or (b) R¹⁰ and R¹¹ are the same and each is a lower alkyl group, a phenyl group (optionally substituted with one or more hydroxy or lower alkoxy groups) or, pyridyl group.

The acid for use in this reaction is conveniently an aqueous inorganic acid, for example hydrochloric acid, having a strength in the range of 0.5 to 2.0 M. Normally the reaction reaches completion after 2 or 3 hours.

The compounds of formula (XIX) are novel and constitute a further aspect of the present invention.

Compounds of formula (I) wherein R² is a lower alkyl group and R¹ is a group CO₂ R in which R is as hereinbefore defined may be converted to pyrimido {4,5-c}pyridazines by treatment with aqueous acid at room temperature. Thus according to yet a further aspect of the present invention there is provided a method of making a compound of formula (XXI): ##STR21## wherein R¹² is a lower alkyl group which comprises treating with aqueous acid at room temperature a compound of formula (XXII): ##STR22## wherein R¹³ is a lower alkyl group and R is as hereinbefore defined.

It should be noted that R¹³ in formula (XXII) becomes R¹² in formula (XXI).

The conditions for this hydrolysis reaction should be mild i.e. carried out without heating, and the acid, which is preferably an inorganic aqueous acid, for example hydrochloric acid, should be added until the reaction medium reaches a pH of 3 or less. Normally the reaction is completed within 2 or 3 days.

The compounds of formula (XXI) are novel and constitute a further aspect of the present invention. The compounds of formula (XXI) may themselves be further converted to a different pyrimido {4,5-c}-pyridazine by boiling in a hydroxylic solvent, for example methyl cellosolve. Thus according to a further aspect of the present invention there is provided a method of making a compound of formula (XXIII): ##STR23## which comprises heating a compound of formula (XXI) in boiling methyl cellosolve. Normally the heating is carried out for up to 24 hours.

The compound of formula (XXIII) is novel and constitutes a further aspect of the present invention.

It should be noted that regardless of the nature of 12 in the substituent at the 4-position in formula (XXI), cleavage normally results in the compound of formula (XXIII) which has a methyl group in its 4-position.

All the starting materials specified above for the various syntheses may be prepared by standard methods taught in the art.

As stated hereinabove the compounds of formula (II) or their tautomers, or salts thereof not only inhibit the growth of micro-organisms to some extent but also unexpectedly act with a potentiating effect when combined with a 2,4-diamino-5-benzylpyrimidine or with a sulphonamide, or with a combination of both these types of antimicrobial agents.

In a further aspect of the present invention therefore there is provided a composition for treating microbial infections, comprising an effective potentiating amount of a compound of formula (II) in combination with an effective amount of a 2,4-diamino-5-benzylpyrimidine, or a sulphonamide, or both.

The microbial infections against which the combinations of this invention are effective are protozoal or bacterial infections caused by those microorganisms which synthesise at least a substantial part of their tetrahydrofolate co-factor requirements. More specifically these infecting microorganisms are those which adequately absorb the pharmaceutical combinations disclosed herein and further are those in which these combinations have a synergistic effect in interfering with the de novo synthesis of the required tetrahydrofolate co-factors.

Also as stated hereinabove the compounds of formula (III), their tautomers and their salts not only inhibit the growth of protozoa but also unexpectedly act with a potentiating effect when combined with a combination of a 2,4-diamino-5-benzylpyrimidine and a sulphonamide.

In a further aspect the invention thus provides a composition for treating protozoal infections comprising an effective potentiating amount of a compound of formula (III) in combination with an effective amount of a combination of a 2,4-diamino-5-benzylpyrimidine and a sulphonamide.

In accordance with the above, the term "an effective amount" used in conjunction with the terms a 2,4-diamino-5-benzylpyrimidine and a sulphonamide means either (a) an amount of the 2,4-diamino-5-benzylpyrimidine or sulphonamide which is effective to a degree as an antimicrobial agent in its own right but which is potentiated by the use of a compound of formula (II), or its tautomer, or salt thereof or (b) an amount of the 2,4-diamino-5-benzylpyrimidine or sulphonamide which is ineffective as an antimicrobial agent but which when combined with a compound of formula (II), or its tautomer, or salt thereof, provides a composition which is an effective antimicrobial agent. An "effective potentiating amount" means an amount of the compound of formula (II), or formula (III), or its tautomer or salt thereof which increases the activity of a 2,4-diamino-5-benzylpyrimidine and/or a sulphonamide so as to provide a greater antimicrobial effectiveness for the whole combination.

The compound of formula (II) or (III) either for use alone or in combination with a 2,4-diamino-5-benzylpyrimidine and/or a sulphonamide may be presented in association with a carrier in pharmaceutical formulations suitable for parenteral, topical, rectal or oral administration. The formulations for oral or rectal administration are advantageously presented in discrete units, such as tablets, capsules, cachets, ampoules or suppositories each containing a predetermined amount of compound, but may also be presented as a powder, as granules, as a solution or suspension in an aqueous or non-aqueous liquid, or as an ointment or paste for topical administration. For parenteral use, the formulations incorporating an aqueous or non-aqueous liquid carrier must be sterile and be presented in sealed containers. The formulations may be made by any of the known methods and may include one or more of the following accessory ingredients: diluents, solutes to render the solution isotonic with the blood, buffers, flavouring, binding, dispersing, surface-active, thickening, lubricating and coating materials, preservatives, bacteriostats, antioxidants, suppository and ointment bases, and any other acceptable excipients.

In another aspect of the present invention, therefore, there is provided a pharmaceutical formulation comprising a compound of formula (II) or (III) alone, or in combination with a 2,4-diamino-5-benzylpyrimidine and/or a sulphonamide, in admixture with a pharmaceutically acceptable carrier. In yet another aspect the present invention provides a method of making a pharmaceutical formulation by admixing the compound of formula (II) or (III) alone, or in combination with a 2,4-diamino-5-benzylpyrimidine and/or a sulphonamide with a carrier by known techniques.

Any of the aforementioned antimicrobial compounds may be presented in the form of their pharmaceutically acceptable salts. Examples of pharmaceutically acceptable salts are those derived from mineral or organic acids, for example hydrochloric acid, hydrobromic acid, sulphuric acid, acetic acid, citric acid, tartaric acid, lactic acid, maleic acid, or salicylic acid, or especially for the sulphonamide, of a base, such as sodium or potassium hydroxide. Salts which are not pharmaceutically acceptable may be rendered so by a conventional metathetical reaction.

In yet another aspect, the present invention provides a method of treating animals suffering from microbial infections which comprises admimistering a non-toxic effective antimicrobial treatment amount of a compound of formula (II) or (III), or preferably administering a pharmaceutical formulation comprising said amount of a compound of formula (II) or (III) and a pharmaceutically acceptable carrier, to the infected animal.

In yet a further aspect, the present invention provides a method of treating animals suffering from microbial infections which comprises administering a composition comprising an effective potentiating amount of a compound of formula (II) or (III), in combination with an effective amount of a 2,4-diamino-5-benzylpyrimidine or a sulphonamide, or both, or preferably administering a pharmaceutical formulation comprising the said composition and a pharmaceutically acceptable carrier, to the infected animal.

A suitable dose range for a compound of formula (II) of formula (III) (either alone or with a sulphonamide and/or pyrimidine derivative) for the treatment of microbial infections lies in the range of 1 mg to 100 mg/kg body weight.

For compounds of formula (III) when used incorporated in animal feeds for the treatment or prophylaxis of protozoal infections a suitable dose range is from 100 to 400 ppm of active ingredient.

Further advantages of the present invention can be ascertained from the following Examples which should not be construed as limiting the scope of the invention in any way.

EXAMPLE 1 8-Amino-3,5-diphenyl-1-methyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one

(I) (R¹ =C₆ H₅ ; R² =C₆ H₅)

To a stirred, refluxing mixture of 6-(1-methylhydrazino)isocytosine hemihydrate (1.00 g) in methanol (100 ml) was added 1,3-diphenyl-1,3-propanedione (2.05 g). After 236 hours the orange solution was allowed to cool to room temperature.

The solution was concentrated under vacuum onto silica gel (5.0 g) that was added to a column of silica gel (90 g) in hexane. Elution of the column with benzene, a 3:1 benzene:chloroform mixture, chloroform, and ethyl acetate effected separation of the desired product that came off in the 3:1 benzene:chloroform mixture, chloroform, and ethyl acetate, yield 1.01 g. Yellow solid was obtained after recrystallisation from carbon tetrachloride, yield 0.64 g (29%): mp 205°-220° dec.; nmr (DMSO-d₆) δ3.12(s, 3H), 6.69(s, 1H), 6.77(br. s, 2H), 7.2-7.6(m, 8H), 7.6-8.0(m, 2H), 10.6(br. s, 1H); uv λ max (CH₃ OH) 255.5 nm (ε22,200), 285(26,400), 385(700), Mass spectrum (210° C.): M, m/e 343. The following accurate mass was determined: 343.1437 (C₂₀ H₁₇ N₅ O).

Anal. Calcd. for C₂₀ H₁₇ N₅ O.0.022 CCl₄ ; C,69.35%; H,4.94%; N,20.20%; Cl, 0.90%. Found: C,69.43%; H,5.09%; N,20.15%; Cl,0.90%.

EXAMPLE 2 8-Amino-1,3,5-trimethyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one

(I) (R¹ =CH₃ ; R² =CH₃)

To a stirred, refluxing mixture of 6-(1-methylhydrazino)isocytosine hemihydrate (1.00 g) in methanol (100 ml) was added acetylacetone (0.913 g). After 48 hours the resulting orange solution was allowed to cool to room temperature and stand overnight.

The solution was concentrated by boiling to 25 ml and was then allowed to cool to room temperature. After 2 hours the slightly cloudy solution was filtered, and the clear filtrate was concentrated by boiling to 15 ml after which time it was allowed to cool to room temperature and stand overnight. No crystallisation occurred until after 24 hours when the solution was suddenly jarred. After an additional 2 hours yellow crystals were collected, washed quickly with methanol (5 ml) and hexane (10 ml), and dried under vacuum at 75° C. to yield the desired product 0.541 g (41%): mp 250°-253° dec; nmr (DMSO-d₆) δ1.84(s, 3H), 2.06 (d, 3H, J=1 Hz), 2.88(s, 3H), 5.89 (q, 1H, J=1 Hz), 6.67(br. s, 2H), 10.58(br. s, 1H). On a different batch of product a Nuclear Overhauser Effect of 25% was observed for the aromatic ##STR24## quartet at 5.89δ upon irradiation of the aromatic --CH₃ doublet at 2.06δ. A Nuclear Overhauser Effect of 19% was observed for the aromatic ##STR25## quartet at 5.89δ upon irradiation of the ring --CH₃ singlet at 1.84δ. A coupling experiment showed that absorption at 2.065 and 5.895 were coupled to each other; uv λ max (CH₃ OH) 233.5 nm sh (ε11,400), 267(17,900), 302(9,900), 348(1,300); pKa 9.11 and 3.27. Mass spectrum of a different batch: M, m/e 219, 43%; m/e 178, 100%.

Anal. Calcd. for C₁₀ H₁₃ N₅ O: C,54.78%; H,5.98%; N,31.95%. Found: C,54.96%; H,5.99%; N,31.72%.

EXAMPLE 3 8-Amino-3-carbomethoxy-5-(3-hydroxyphenyl)-1-methyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one

(I) (R¹ =C₆ H₄ OH; R² =CO₂ CH₃)

To a stirred, refluxing mixture of 6-(1-methyl hydrazino)isocytosine hemihydrate (1.76 g) in methanol (176 ml) was added methyl m-hydroxybenzoylpyruvate (2.88 g). After 22 hours precipitated solid was collected from the hot mixture, yield 0.282 g.

The filtrate was brought to boiling and was concentrated to 75 ml when precipitated solid was noticed to be present. The mixture was allowed to cool to room temperature and stand for several hours. Brownish-orange solid was collected, washed with two portions of methanol (10 ml each), and dried under vacuum at 80° C. to yield the desired product 1.80 g (49%): mp >275° dec; nmr (DMSO-d₆) δ3.11(s, 3H), 3.79(s, 3H), 6.50(s, 1H), 6.6-7.4 (m, 6H), 9.22(br. s, 1H), 10.77(br. s, 1H); uv λ max (CH₃ OH) 244.5 nm (ε19,600), 280.5 sh (16,700), 305(20,500), 424(700).

Anal. Calcd. for C₁₆ H₁₅ N₅ O₄ : C,56.30%; H,4.43%; N,20.52%. Found: C,56.34%; H,4.48%; N,20.56%.

EXAMPLE 4 8-Amino-3-carbomethoxy-1-methyl-5-(3-pyridyl)-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one

(I) (R¹ =3-pyridyl; R² =CO₂ CH₃)

To a stirred, refluxing mixture of 6-(1-methylhydrazino)isocytosine hemihydrate (1.00 g) in methanol (100 ml) was added methyl 2,4-dioxo-4-(3-pyridyl)butyrate (1.51 g). After 171/2 hours brown solid was collected from the hot mixture, washed with two portions of methanol (10 ml each), and dried under vacuum at 75° C. to yield the desired product 1.11 g (56%): mp 258°-272° dec; nmr (DMSO-d₆) δ3.11(s, 3H), 3.79(s, 3H), 6.56(s, 1H), 6.98(br. s, 2H), 7.1-7.8(m, 2H), 8.3-8.6(m, 2H), 10.9(br. s, 1H); nmr (CF₃ COOH) δ3.53(s, 3H), 4.12(s, 3H), 7.13(s, 1H), 8.0-8.3(m, 1H), 8.5-9.0(m, 3H); uv λ max (CH₃ OH) 244.5 nm (ε21,800), 284 sh(16,500), 307.5(17,500), 454(900).

Anal. Calcd. for C₁₅ H₁₄ N₆ O₃ : C,55.21%; H,4.32%; N,25.76%. Found: C,55.19%; H,4.29%; N,25.84%.

EXAMPLE 5 8-Amino-3-carbethoxy-1-methyl-5-phenyl-1H-pyrimido-{4,5-c}-1,2-diazepin-6(7H)-one

(I) (R¹ =C₆ H₅ ; R² =CO₂ C₂ H₅)

To a stirred mixture of 6-(1-methylhydrazino)isocytosine hemihydrate (1.00 g) in absolute ethanol at 65°-70° was added ethyl benzoylpyruvate (2.01 g). After 101 hours some precipitated solid was collected from the hot mixture. After a further 1/2 hour an additional small amount of solid was filtered from from cooled filtrate.

After the filtrate had stood overnight, precipitated pale orange solid was collected, washed with 5 ml of chloroform and 10 ml of hexane, and dried under vacuum at 75° to yield the desired product 0.796 g. Yellow solid was obtained after two recrystallizations from benzene, yield 0.200 g (9%): mp 240.5°-242.5° dec; nmr (DMSO-d₆) δ1.28(t, 3H), 3.12(s, 3H), 4.26(q, 2H), 6.52(s, 1H), 6.89(br. s, 2H), 7.28(br. s, 5H), 10.7 (br. s, 1H); uv λ max (CH₃ OH) 243.5 nm (ε19,400), 294(20,200), 419.5(600). Mass spectrum (180° C.): M, m/e 339, 35%; m/e 240, 100% (M--C₂ H₅ O₂ CCN). The following accurate mass was determined: 240.1008 (C₁₃ H₁₂ N₄ O). The most prominent metastable ion for the molecular ion was m/e 339→m/e 240.

Anal. Calcd. for C₁₇ H₁₇ N₅ O₃.0.20C₆ H₆ : C,61.58%; H,5.17%; N,19.73%. Found: C,61.72%; H,5.29%; N,19.88%.

EXAMPLE 6 8-Amino-3-carbomethoxy-1-methyl-5-(3,4,5-trimethoxyphenyl)-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one

(I) (R¹ =C₆ H₂ (OCH₃)₃ ; R² =CO₂ CH₃)

To a stirred, refluxing mixture of 6-(1-methyl hydrazino)isocytosine hemihydrate (1.00 g) in methanol (100 ml) was added methyl 3,4,5-trimethoxybenzoylpyruvate (2.70 g). After 40 hours precipitated solid was collected from the hot mixture to yield 0.360 g of product.

The filtrate was concentrated under vacuum to 2.8 g of solid that was stripped onto silica gel (5.0 g) that was added to a column of silica gel (90 g) in hexane. Elution of the column with benzene, benzene:chloroform mixtures, chloroform, a 1:1 chloroform:ethyl acetate mixture, ethyl acetate, and finally a 9:1 ethyl acetate:methanol mixture effected separation of the desired product that came off in the 9:1 ethyl acetate:methanol mixture, yield 1.57 g. Tiny, orange crystals were obtained after recrystallisation from methanol to yield 1.15 g (45%) of product; mp 258°-260° dec.; nmr (DMSO-d₆) δ3.09(s, 3H), 3.67, 3.74, and 3.77 (overlapping s's, 12H), 6.47(s, 2H), 6.51(s, 1H), 6.87(br. s, 2H), 10.8(br. s, 1H); uv λ max (CH₃ OH) 239 nm sh (ε19,900), 307.5 (24,600), 421(800). Mass spectrum of a different batch (210° C.): M, m/e 415, 56%; m/e 330, 57%; m/e 315, 100%.

Anal. Calcd. for C₁₉ H₂₁ N₅ O₆ : C,54.93%; H,5.10%; N,16.86%. Found: C,54.99%; H,5.15%; N,16.82%.

The following compounds were prepared in a manner similar to that of Example 6:

EXAMPLE 7 8-Amino-3-carbethoxy-1-methyl-5-(2,4-dimethoxyphenyl)-1H-pyrimido {4,5-c}-1,2-diazepin-6(7H)-one

(I) (R¹ =C₆ H₃ (OCH₃)₂ ; R² =CO₂ C₂ H₅)

Refluxing absolute ethanol was used as solvent. Precipitated solid was collected after 42 hours. Product was eluted from a column with 9:1 ethyl acetate:methanol.

Yield after recrystallisation from benzene (28%): mp 187°-196° dec.; nmr (DMSO-d₆) δ1.27(t, 3H), 3.09(s, 3H), 3.64(s, 3H), 3.77(s, 3H), 4.24(q, 2H), 6.4-7.1(m, 6H), 10.5(br s, 1H); uv λ max (CH₃ OH) 246.5 nm (ε20,500), 311.5(21,700), 345.5 sh (5,100) 420 sh (900).

Anal. Calcd. for C₁₉ H₂₁ N₅ O₅.0.43 C₆ H₆ : C, 59.86%; H, 5.49%; N, 16.18%. Found: C, 59.89%; H, 5.54%; N, 16.33%.

EXAMPLE 8 8-Amino-3-carbethoxy-1-methyl-5-(3,4-dimethoxyphenyl)1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one

(I) (R¹ =C₆ H₃ (OCH₃)₂ ; R² =CO₂ C₂ H₅)

Absolute ethanol (65°-70° C.) was used as solvent. Precipitated solid was collected after 112 hours. Product was eluted from a column with ethyl acetate. Yield after dissolution in ethyl acetate and precipitation with hexane (7%): mp 162° dec; nmr (DMSO-d₆) δ1.27(t, 34), 3.10(s, 3H), 3.72(s, 3H), 3.75 (s, 3H), 4.24(q, 2H), 6.50(s, 1H), 6.6-7.2(m, 5H), 10.8(br s, 1H); uv λ max (CH₃ OH) 245 nm (ε20,800), 309 (21,900).

Anal. Calcd. for C₁₉ H₂₁ N₅ O₅.0.1 CH₃ CO₂ C₂ H₅. 0.4 H₂ O: C, 56.09% H, 5.48%; N, 16.86%. Found: C, 56.16%; H, 5.23%; N, 16.86%.

EXAMPLE 9 8-Amino-3-carbethoxy-1,5-dimethyl-1H-pyrimido{4,5c}-1,2-diazepin-6(7H)-one

(I) (R¹ =CH₃ ; R² =CO₂ C₂ H₅)

To a stirred, refluxing mixture of 6-(1-methylhydrazino)isocytosine hemihydrate (5.00 g) in methanol (500 ml) was added ethyl acetylpyruvate (5.78 g). After 65 hours the solution was concentrated by boiling to 40 ml and was allowed to stand overnight.

The solution was concentrated under vacuum to 9.7 g of pasty solid that was stripped onto silica gel (10 g) that was then added to a column of silica gel (400 g) in hexane. Elution of the column with a 1:1 benzene:chloroform mixture, chloroform, chloroform:ethyl acetate mixtures, ethyl acetate, and a 4:1 ethyl acetate:methanol mixture effected separation of desired product that came off in ethyl acetate, yield 3.95 g. Orange crystals were obtained after recrystallisation from ethyl acetate, yield 2.52 g (30%): mp 244°-245° dec; nmr (DMSO-d₆) δ1.24 (t, 3H, J=7.5 Hz), 2.12(d, 3H, J=1 Hz), 3.03(s, 3H), 4.22(q, 2H, J=7.5 Hz), 6.18(q, 1H, J=1 Hz), 6.83(br s, 2H), 10.8(br s, 1H). On a different batch of product, a Nuclear Overhauser Effect of 32% was observed for the aromatic ##STR26## quartet at 6.18δ upon irradiation of the aromatic --CH₃ doublet at 2.12δ; uv of a different batch λ max (CH₃ OH) 245 nm (ε17,200), 284 sh (11,300), 306(14,100), 410(600). Mass spectrum of a different batch (155° C.): M, m/e 277, 29%; m/e 178, 100% (M-NCCO₂ C₂ H₅). The following accurate masses were determined 277.1163(C₁₂ H₁₅ N₅ O₃), 178.0843(C₈ H₁₀ N₄ O).

Anal. Calcd. for C₁₂ H₁₅ N₅ O₃ : C, 51.98%; H, 5.45%; N, 25.26%. Found: C, 51.91%; H, 5.45%; N, 25.18%.

EXAMPLE 10 8-Amino-5-carbethoxy-1,3-dimethyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one

(I) (R¹ =CO₂ C₂ H₅ ; R² =CH₃)

The isomer of the compound just described was prepared and isolated in the same experiment.

This product came off the column in ethyl acetate and a 4:1 ethyl acetate:methanol mixture after its isomer (previous Example) had came off, yield 3.13 g. Pale yellowish-orange crystals were obtained after two recrystallisations from carbon tetrachloride, yield 0.942 g (11%): mp 196° dec; nmr (DMSO-d₆) δ1.16(t, 3H), 1.93(s, 3H), 2.91(s, 3H), 4.06(q, 2H), 6.39(s, 1H), 6.83(br s, 2H), 10.8(br s, 1H), uv of a different batch λ max (CH₃ OH) 241.5 nm (ε14,500), 295(14,200), 305.5 sh (13,100), 387(900). Mass spectrum of a different batch (160°): M, m/e 277, 70%; m/e 236, 100% (M-CH₃ CN). The following accurate masses were determined: 277.1170 (C₁₂ H₁₅ N₅ O₃), 236.0902 (C₁₀ H₁₂ N₄ O₃).

Anal. Calcd. for C₁₂ H₁₅ N₅ O₃.0.45 CCl₄ : C, 43.15%; H, 4.36%; N, 20.21%; Cl, 18.42%. Found: C, 42.87%; H, 4.38%; N, 20.43%; Cl, 18.07%.

EXAMPLE 11 2,7-Diamino-8-methyl-5-phenylpyrido{2,3-d}pyrimidin-4(8H)-one

(XVII) (R⁸ =C₆ H₅)

To 8-amino-3-carbethoxy-1-methyl-5-phenyl-1H-pyrimido {4,5-c}-1,2-diazepin-6(7H)-one (2.9 g) was added N NaOH (100 ml), and a solution resulted after the mixture was swirled. After 45 minutes the solution was acidified with conc. HCl until pH 2.5-3.0 was reached. Precipitated yellow solid was collected, washed with water (3×15 ml), and dried under vacuum at 70° C., yield 2.4 g of product. This solid was shown by nmr to be the corresponding carboxylic acid of the starting ester.

A 2.3 g sample of solid was suspended in boiling methyl cellosolve (175 ml), and the resulting dark brownish-red solution quickly became orangish-yellow in colour. The solution was concentrated to 130 ml when solid precipitated. The mixture was allowed to cool to room temperature and stand for 2 hours. Off-white solid was collected, washed with methyl cellosolve (2×15 ml) and methanol (4×15 ml), and dried under vacuum at 70° C., yield 1.28 g (49%) of product: mp>300°; nmr (CF₃ COOH) δ4.08(s, 3H), 6.68(s, 1H), 7.0-7.8(m, 7H); nmr (DMSO-d₆) δ3.64(s, 3H), 5.93(s, 1H), 6.76 (br s, 2H), 7.1-7.4(m, 5H), 7.8* (very br s, 2H); uv λ max (CH₃ OH) 216 nm (ε35,300), 258 sh (9,400), 290.5(13,000), 348(17,400). Mass spectrum (250°): M, m/e 267, 100%; m/e 266, 26%; m/e 140, 10%. The following accurate mass was determined: 267.1120(C₁₄ H₁₃ N₅ O).

Anal. Calcd. for C₁₄ H₁₃ N₅ 0.0.08 CH₃ OCH₂ CH₂ OH.0.2 H₂ O: C, 61.75%; H, 5.11%; N, 25.29%. Found: C, 61.76%; H, 5.30%; N, 25.32%.

EXAMPLE 12 2,7-Diamino-8-methyl-5-(3-hydroxyphenyl)pyrido{2,3-d}-pyrimidin-4(8H)-one

(XVII) (R⁸ =C₆ H₄ OH)

To 8-amino-3-carbomethoxy-1-methyl-5-(3-hydroxyphenyl)-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one (4.79 g) was added N NaOH (190 ml), and a solution resulted after the mixture was swirled. After 1 hour 15 minutes the solution was acidified with conc. HCl until pH 1 was reached. Precipitated solid was collected, washed with water (3×10 ml), and dried under vacuum at 80° C. to yield 4.49 g of product. This solid was shown by nmr to be the corresponding carboxylic acid of the starting ester.

The carboxylic acid was boiled for 21/2 hours in methyl cellosolve (50 ml), and product was collected from a hot mixture, washed with methyl cellosolve (15 ml) and methanol (3×10 ml), and dried under vacuum at 80°, yield (60%): mp>300°; nmr (CF₃ COOH): δ4.07(s, 3H), 6.69(s, 1H), 7.0-7.6(m, 6H); uv λ max (CH₃ OH) 217.5 nm (ε42,300), 247 sh (10,700), 292 (14,300), 338 weak sh (16,200), 347(18,400).

Anal. Calcd. for C₁₄ H₁₃ N₅ O₂ : C, 59.35%; H, 4.63%; N, 24.72%. Found: C, 59.24%; H, 4.65%; N, 24.70%.

EXAMPLE 13 2,7-Diamino-8-methyl-5-(3,4,5-trimethoxyphenyl)pyrido{2,3-d}pyrimidin-4(8H)-one

(XVII) (R⁸ =C₆ H₂ (OCH₃)₃)

Following the general procedure of Example 11, the above compound was synthesised.

Yield (55%): mp>300°; nmr (CF₃ COOH) δ4.00 (s, 6H), 4.09(s, 6H), 6.73(s, 1H), 6.76(s, 2H), 7.26 (br s, 2H); uv λ max (CH₃ OH) 261.5 nm (ε10,400), 293(14,000), 339 weak sh (16,900), 348(18,800). Mass spectrum (260°): M, m/e 357, 100%; m/e 342, 16% (M-CH₃); m/e 327, 4% (M-CH₂ O and M-C₂ H₆); m/e 317, 1% (M-C₂ H₂ N); m/e 316, 1% (M-C₂ H₃ N).

The following accurate masses were determined: 357.1432(C₁₇ H₁₉ N₅ O₄), 342.1203(C₁₆ H₁₆ N₅ O₄), 327.1333 (C₁₆ H₁₇ N₅ O₃), 327.0969(C₁₅ H₁₃ N₅ O₄), 317.1265(C₁₅ H₁₇ N₄ O₄), 316.1164(C₁₅ H₁₆ N₄ O₄).

Anal. Calcd. for C₁₇ H₁₉ N₅ O₄ : C, 57.13%; H, 5.36%; N, 19.60%. Found: C, 57.15%; H, 5.41%; N, 19.52%.

The reaction was shown to procede through the intermediate carboxylic acid. This acid was identified by nmr and gave the following microanalysis: Calcd. for C₁₈ H₁₉ N₅ O₆ : C, 53.86; H, 4.77; N, 17.45%. Found: C, 53.90; H, 4.80; N, 17.34%.

EXAMPLE 14 2,7-Diamino-5,8-dimethylpyrido{2,3-d}pyrimidin-4(8H)-one

(XVII) (R⁸ =CH₃)

Following the general procedure of Examples 11 and 12, the above compound was synthesised.

Yield (68%): mp>300°; nmr (CF₃ COOH) δ2.81 (s, 3H), 4.00(s, 3H), 6.65(s, 1H), 6.96(br s, 2H); nmr (DMSO-d₆) δ2.54 (s, 3H), 3.61(s, 3H), 5.98(s, 1H), 6.49 (br s, 2H), 7.5* (very br s, 2H); uv λ max (CH₃ OH) 218 nm (ε31,100), 253 (4,300), 290.5 (8,400), 327.5 sh (17,300), 337(20,400). Mass spectrum (250° C.): M, m/e 205, 100%; m/e 165, 4% (M-C₂ H₂ N); m/e 164, 3% (M-C₂ H₃ N). The following accurate masses were determined: 205.0962(C₉ H₁₁ N₅ O), 165.0785(C₇ H₉ N₄ O), 164.0709(C₇ H₈ N₄ O).

Anal. Calcd. for C₉ H₁₁ N₅ O: C, 52.67; H, 5.40; N, 34.13%. Found: C, 52.50; H, 5.40; N, 34.05%.

EXAMPLE 15 2,7-Diamino-8-methyl-5-(3-pyridyl)pyrido{2,3-d}-pyrimidin-4(8H)-one

(XVII) (R⁸ =3-pyridyl)

The above compound was synthesised following the general procedure of Examples 11 and 12.

Yield (27%): mp 301°-304° dec; nmr (CF₃ COOH) δ4.12(s, 3H), 6.85(s, 1H), 7.69(br s, 2H), 8.1-8.4 (m, 1H), 8.6-9.1 (m, 3H); uv λ max (CH₃ OH) 215 nm (ε34,800), 264.5(11,300), 290(10,800), 352.5 (15,900). Mass spectrum: M, m/e 268, 100%; m/e 240, 10%; m/e 228, 3% (M-C₂ H₂ N); m/e 227, 3% (M-C₂ H₃ N and M-CHN₂). The following accurate masses were determined: 268.1072 (C₁₃ H₁₂ N₆ O), 228.0885 (C₁₁ H₁₀ N₅ O), 227.0923 (C₁₂ H₁₁ N₄ O), 227.0811 (C₁₁ H₉ N₅ O).

Anal. Calcd. for C₁₃ H₁₂ N₆ O.0.24 CH₃ OCH₂ CH₂ OH. 0.18 H₂ O: C, 56.86%; H, 4.97%; N, 29.00%. Found: C, 56.82%; H, 5.08%; N, 29.05%.

EXAMPLE 16 6-Amino-1,3-dimethyl-1H-pyrazolo{3,4-d}pyrimidin-4(5H)-one

(XIX) (R⁹ =CH₃)

A mixture of 8-amino-1,3,5-trimethyl-1H-pyrimido-{4,5-c}-1,2-diazepin-6(7H)-one (219 mg) and N hydrochloric acid (3 ml) was heated using a hot water bath (>85° C.) for 2 hours. During that period a solution formed before crystals gradually began to separate. The mixture stood at room temperature overnight before the straw-coloured crystals were collected, washed with water and dried under vacuum (70° C.) to yield 140 mg (78%) of analytically pure product: mp >300°; nmr (DMSO-d₆) δ2.28(s, 3H), 3.60(s, 3H), 6.52(br s, 2H), 10.30(br s, 1H); uv λ max (CH₃ OH) 217 nm (ε26,800), 254(13,000). Mass spectrum (120° C., 70 ev): M, m/e 179, 100%.

Anal. Calcd. for C₇ H₉ N₅ O: C, 46.92%; H, 5.06%; N, 39.09%. Found: C, 46.68%; H, 5.11%; N, 38.94%.

The following compounds (Examples 17, 18 and 19) were prepared by similar acid-catalysed hydrolysis conditions:

EXAMPLE 17 6-Amino-1-methyl-3-phenyl-1H-pyrazolo{3,4-d}pyrimidin-4(5H)-one

(XIX) (R⁹ =C₆ H₅)

Method A

Starting material, 8-amino-3-carbethoxy-1-methyl-5-phenyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one; reaction time, 3 hours; yield after recrystallisation from ethanol, 43%: mp>300°; nmr (DMSO-d₆) δ3.73 (s, 3H), 6.65 (br s, 2H), 7.30-7.50(m, 3H), 8.25-8.42 (m, 2H), 10.90(br, s, 1H); uv λ max (CH₃ OH) 246 nm (ε29,900), 280 sh (8,400). Mass spectrum (170°, 70 ev): M, m/e 241, 100%.

Anal. Calcd. for C₁₂ H₁₁ N₅ O: C, 59.74%; H, 4.60%; N, 29.03%. Found: C, 59.60%; H, 4.66%; N, 28.92%.

Method B

Starting material, 8-amino-3,5-diphenyl-1-methyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one; reaction time, 3 hours; yield after washing with ether,* 29%: spectral data same as that recorded above.

Anal. Found: C, 59.47%; H, 4.59%; N, 28.77%.

EXAMPLE 18 6-Amino-1-methyl-3-(3,4,5-trimethoxyphenyl)-1H-pyrazolo{3,4-d}pyrimidin-4(5H)-one

(XIX) (R⁹ =C₆ H₂ (OCH₃)₃)

Starting material, 8-amino-3-carbomethoxy-1-methyl-5-(3,4,5-trimethoxyphenyl)-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one; reaction time, 3 hours; yield after subsequent neutralization of the collected, crude product with 0.1 N sodium hydroxide and recrystallisation from methanol, 40%: mp 183°-184°; nmr (DMSO-d₆) δ3.70(s, 3H), 3.77(s, 3H), 3.85(s, 6H), 6.70(br s, 2H), 7.87(s, 2H), 10.43(br s, 1H) plus methanol δ3.19(d, 3H, J=5 Hz), 4.04(q, 1H, J=5 Hz); uv λ max (CH₃ OH) 222.5 nm (ε33,200), 254.5 (24,100), 282 (14,800). Mass spectrum (160°, 70 ev): M, m/e 331, 100%*. 6 *This mass spectrum was obtained for a different batch prepared by the same method.

Anal. Calcd. for C₁₅ H₁₇ N₅ O₄.CH₃ OH: C,52.89%; H,5.83%; N,19.27%. Found: C,52.73%; H,5.63%; N,19.45%.

EXAMPLE 19 6-Amino-3-(3-hydroxyphenyl)-1-methyl-1H-pyrazolo-{3,4-d}pyrimidin-4(5H)-one.0.55 methanolate.0.16 hydrate

(XIX) (R⁹ =C₆ H₄ OH)

Starting material, 8-amino-3-carbomethoxy-5-(3-hydroxyphenyl)-1-methyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one; reaction time, 2 hours. A solid impurity was removed by filtration before the crude product was subsequently precipitated from the mother liquor by neutralization with 4 N sodium hydroxide solution, collected by filtration, washed with water, dried under vacuum (70°) and recrystallised twice from methanol; yield,* 21%: mp>300°; nmr (DMSO-d₆) δ3.74(s, 3H), 6.67 m and 6.80 m (3H), 7.21(t, 3H, J=8 Hz), 7.81 m and 7.89 m (2H), 9.36(s, 1H), 10.56(br s, 1H) plus methanol (0.5 mol) 3.19(d, 3H, J=5 Hz), 4.04(q, 1H, J=5 Hz) and water δ3.30; uv λ max (CH₃ OH) 248 nm (Ε26,400), 248 sh (8,800). Mass spectrum (150°, 70 ev): M, m/e 257, 100%. ≠*Other batches obtained during recrystallisation provided evidence for an overall yield of ca. 40%.

Anal. Calcd. for C₁₂ H₁₁ N₅ O₂.0.55 CH₃ OH.O.16H₂ O: C,54.27%; H,4.91%; N,25.22%. Found: C,54.25%; H,4.82%; N,25.20%.

Example 20 4-Acetonyl-7-amino-1-methylpyrimido{4,5-c}pyridazine-3,5-(1H, 2H)-dione

(XXI) (R¹² =CH₃)

A solution of 8-amino-5-carbomethoxy-1,3-dimethyl-1H-pyrimido{4,5-c}-1,2-diazepin-6(7H)-one (0.407 g) in a strongly acidic (pH≦2), aqueous solution of HCl (13 ml) was allowed to stand for one day. Precipitated brownish-orange solid was collected, washed with water, and dried under vacuum at 75° C. to yield 0.080 g of a product mixture.

After an additional three days brownish-orange solid in the filtrate was collected, washed with two portions of water (2×2.5 ml) and dried under vacuum at 75° C. to yield 0.097 g (25% of product: nmr (CF₃ COOH) δ2.60(s, 3H), 4.28(s, 3H), 4.85(s, 2H), 6.92(br s, 2H). Qualitative uv data and the nmr data suggested that the compound had the structure named above.

EXAMPLE 21 7-Amino-1,4-dimethylpyrimido{4,5-c}pyridazine-3,5-(1H, 6H)-dione

(XXIII)

4-Acetonyl-7-amino-1-methylpyrimido{4,5-c}-pyridazine-3,5-(1H, 2H)-dione (0.054 g) was dissolved in boiling methyl cellosolve (1 l), and the solution was concentrated to 40 ml when precipitated solid was noticed to be present. The mixture was allowed to cool to room temperature and stand overnight. Yellowish-green solid was collected, washed with methyl cellosolve (10 ml) methanol (2 ml), and dried under vacuum at 75° C. to yield 0.018 g (35%) of product: nmr (CF₃ COOH) δ3.03(s, 3H), 4.26(s, 3H),6.83(br s, 2H).

EXAMPLE 22

The antibacterial activity against Staphylococcus aureus of trimethoprim (TMP) and sulphamethoxazole (SMX) alone and in combination with compounds of formula (II) were compared.

The results shown in the table are expressed as an activity index which is: ##EQU1## the effect of the compounds being measured by viable counts after 24 hours incubation of 10⁶ organisms per ml.

In this test, the compounds of formula (II) were present at 50 μg/ml.

An activity index ≧2 is indicative of substantial potentiation:

    ______________________________________                                         Compound of formula II                                                         R.sup.3    R.sup.4      TMP       SMX                                          ______________________________________                                         C.sub.6 H.sub.5                                                                           CO.sub.2 C.sub.2 H.sub.5                                                                    2.0       >2.8                                         C.sub.6 H.sub.4 OH(3)                                                                     CO.sub.2 CH.sub.3                                                                           0.9       2.7                                          ______________________________________                                    

EXAMPLE 23

The anti-coccidial activity of compounds of formula (III) alone and in combination with a mixture of diaveridine (DV) and sulphaquinoxaline (SQX) in vitro was tested according to the following procedure.

Using standard test procedures employing primary explant cultures of chick embryo liver cells and a suspension of Eimeria tenella (Weybridge) sporozites the activity of the compounds was determined at various concentrations. In the above test, each test compound was used either alone or in combination with sulphaquinoxaline (0.01 μg/ml) and diaveridine (0.031 μg/ml). It should be noted that the minimum active anti-coccidial amounts of sulphaquinoxaline and diaveridine are 0.024 μg/ml and 0.098 μg/ml respectively.

The following results were obtained wherein activity is expressed as follows:

5=No parasite development

4=1-25% parasite development

3=26-50% parasite development

2=51-75% parasite development

1=76-95% parasite development

0=95-100% parasite development

    ______________________________________                                         Compound of formula (III)                                                                        Activity (concentration μg/ml)                            R.sup.3      R.sup.4  Alone    With DV/SQX                                     ______________________________________                                          ##STR27##   CO.sub.2 C.sub.2 H.sub.5                                                                4(100) 4(25) 2(6.25) 0(1.56)                                                            5(100) 5(25) 3(6.25) 2(1.56)                     ##STR28##   CO.sub.2 CH.sub.3                                                                       3(100) 3(25) 3(6.25) 2(1.56)                                                            5(100) 4(25) 3(6.25) 3(1.56)                    C.sub.6 H.sub.5                                                                             C.sub.6 H.sub.5                                                                         4(25)    4(25)                                           ______________________________________                                    

EXAMPLE 24

Compounds of formula (III) were tested for anti-coccidial activity in vivo in combination with diaveridine (DV) and sulphaquinoxaline (SQX), each at 20 ppm, according to the following procedure.

Groups of five, one week old chicks were each injected orally with 6,000 sporulated o cysts of the Weybridge strain of Eimeria tenella. Drugs were administered in LD 5 chick mash deficient in Vitamin K, beginning on the day of infection and continuing for 7 days. On the sixth day after infection, caecal lesions of surviving chicks were scored on a scale of 0, 1, 2 or 3 and any dead chicks were scored as 4. The following results were obtained:

    __________________________________________________________________________     Compound of formula (III)                                                                      Concn. in                                                                            Concn. DV in                                                                           Concn. SQX in                                                                          Lesion                                   R.sup.3    R.sup.4                                                                             diet (ppm)                                                                           diet (ppm)                                                                             diet (ppm)                                                                             score                                    __________________________________________________________________________     --         --   --    20      20      2.2                                       ##STR29## CO.sub.2 C.sub.2 H.sub.5                                                            200   20      20      1.2                                       ##STR30## CO.sub.2 CH.sub.3                                                                   200   20      20      0.6                                      __________________________________________________________________________

EXAMPLE 25

By standard techniques the LD₅₀ values of the following compounds of formula (I) were determined in mice.

    ______________________________________                                         Compound of formula (I)                                                        R.sup.1       R.sup.2     LD50 i.p. in mice                                    ______________________________________                                          ##STR31##    CO.sub.2 CH.sub.3                                                                          > 500 mg/kg                                          CH.sub.3      CH.sub.3    ≃ 500 mg/kg                            ______________________________________                                    

EXAMPLE 26

(i) Tablets containing the following amounts of active ingredients are prepared by standard methods of pharmacy.

(A) Compound of Example 1: 100 mg

(B) Compound of Example 3: 50 mg

(C) Compound of Example 5: 40 mg

Sulphamethoxazole: 400 mg

Trimethoprim: 80 ng

(ii) An animal feed containing the following active ingredients is prepared.

Compound of Example 6: 200 ppm

Sulphamethoxazole: 20 ppm

Trimethoprim: 20 ppm 

What is claimed is:
 1. A method of potentiating the antibacterial activity of a 2,4-diamino-5-benzylpyrimidine and/or sulphamethoxazole against Staphylococcus aureus bacteria which comprises applying to Staphylococcus aureus bacteria an effective antibacterial amount of a 2,4-diamino-5-benzylpyrimidine and/or sulphamethoxazole and an effective potentiating amount of a compound of formula II or a tautomer or a pharmaceutically acceptable salt thereof ##STR32## wherein R³ is phenyl, phenyl substituted with one or more hydroxy and R⁴ is a group --CO₂ R where R is lower alkyl.
 2. The method of claim 1 in which the compound is 8-amino-3-carbethoxy-1-methyl-5-phenyl-1H-pyrimido[4,5-c]-1,2-diazepin-6(7H)-one or 8-amino-3-carbomethoxy-1-methyl-5-(3-hydroxyphenyl-1H-pyrimido[4,5-c]-1,2,diazepin-6[7H]-one.
 3. The method of claim 1 or 2 in which the 2,4-diamino-5-benzyl pyrimidine is trimethoprim.
 4. The method of treating coccidiosis in a chicken which comprises orally administering to said chicken an effective anticoccidiosis amount of a compound of formula III or a tautomer or a pharmaceutically acceptable salt thereof ##STR33## wherein R' is phenyl, phenyl substituted with one or more lower alkoxy and R" is selected from phenyl and --CH₂ R in which R is lower alkyl either alone or in combination with sulphaquinoxaline and/or a 2,4-diamino-5-benzylpyrimidine in an effective potentiating amount.
 5. The method of claim 4 in which R³ is ##STR34## and R⁴ is CO₂ C₂ H₅.
 6. The method of claim 3 in which R³ is ##STR35## and R⁴ is CO₂ CH₃.
 7. The method of claim 1 in which R³ and R⁴ are both C₆ H₅.
 8. The method of claims 6 or 7 in which the 2,4-diamino-5-benzyl pyrimidine is trimethoprim. 